GD32F20x User Manual
723
Precharge delay (PRD) and row to column delay (RCD) are added according to their
configuration in EXMC_SDTCFGx register, other timing parameters should be configured as
SDRAM specification requires.
When this boundary happens to be at the end of a bank, two cases are possible:
1.
When the current bank is not the last bank, the activation of the first row of the next bank
is performed, and this supports all row, column, and bus width configuration.
2.
When the current bank is the last bank, and row, column, and bus width are configured
as, 13-bit, 11-bit, and 32-bit respectively, EXMC continues to read/write from the second
SDRAM device (SDRAM device 1), assuming that the current SDRAM is device 0.
Low power modes
Two low power mode are supported:
1.
Self-refresh mode: In self-refresh mode, refresh is provided by the SDRAM itself to
maintain data integrity without external clock (EXMC_SDCLK). It is entered by writing
0b101 to CMD bits in EXMC_SDCMD register, DS0 andDS1 determines which SDRAM
device will receive the command. EXMC_SDCLK stops running after a RASD delay if
this command is issued to both SDRAM devices or one of the SDRAM device is not
initialized.
2.
Power-down mode: In power-down mode, refresh is provided by the SDRAM controller.
It is entered by writing 0b110 to CMD bits in EXMC_SDCMD register, DS0 and DS1
determines which SDRAM device will receive the command. If the write data FIFO is not
empty, all data are sent to the memory before activating power-down mode.
The Command Mode FSM also controls the switching process of between the normal mode
and the low-power modes (self-refresh/power-down).
The SDRAM controller returns to normal mode from self-refresh mode when a read/write
access occurs. If a read/write access occurs while the SDRAM controller is entering self-
refresh mode, the self-refresh entry process will be interrupted, and the SDRAM controller
remains in normal mode after the read/write access completed.
Figure 25-37. Process for self-refresh entry and exit
Command
Clock
(EXMC_SDCLK)
Clock Enable
(EXMC_SDCKE])
PreA
NOP
ARef
NOP
ARef
NOP
Self-refresh Entry
Self-refresh Exit
If an auto-refresh request occurs when the SDRAM controller is in power-down mode, the
SDRAM controller returns to normal mode, issues the Precharge all and Auto-Refresh
command sequence, and enters power-down mode again automatically.
Содержание GD32F20 Series
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